Keying circuit



RF Currier Feb. 25, 1958 Inpui J. L. JOHNSON KEYING CIRCUIT Filed Oct. 29, 1954 WlTNESSES'.

INVENT'OR John L.Johnsoh.

' ATTORNEY KEYING CIRCUIT John L. Johnson, Rock Hill Beach, Md., assignor to Westmghouse Electric Corporation, East Pittsburgh, Pa, a corporation of Pennsylvania Application October 29, 1954, Serial No. 465,502 Claims. (Cl. 250-27) or both. Generally the source of D. C. blocking voltage will be of a positive polarity and, in some installations, its magnitude may vary considerably. It may, however, become desirable or necessary to apply a negative blocking voltage to one or more grids and to maintain the magnitude of the blocking voltage constant regardless of the magnitude of the source of D. C. voltage pulses.

Accordingly, it is an object of my invention to provide a novel keying circuit which will cut-off one or more vacuum tubes with a constant blocking voltage regardless of the magnitude of the available source of keying voltage.

Another object of my invention lies in the provision of novel means for reversing the polarity of positive D. C. pulses before applying the same to the grid of a vacuum tube.

A still further object of my invention is to provide a novel keying circuit which will apply a blocking voltage to the grids of two or more vacuum tubes in accordance with variations in a single input keying voltage.

The above and other objects and features of my invention will become apparent from the following description taken in connection with the accompanying single figure drawing which illustrates the invention schematically.

Referring to the drawing, it can be seen that a triode vacuum tube is connected between the terminals of a source of D. C. voltage 12. Connected between the anode 14 of tube 10 and the positive terminal of source 12 is a first resistor 16. A second resistor 18 is connected between the negative terminal of source 12 and 1 the cathode 20 of tube 10.

In paralllwith tube 10 are a pair of serially connected gaseous discharge tubes or rectifiers 22 and 24. The anode of tube 22 is connected via resistor 16 to the positive terminal of source 12; likewise, the cathode of tube 24 is connected via resistor 18 to the negative terminal of source 12. A second pair of serially connected gaseous discharge tubes 26 and 28 are connected in parallel with tube 10 in a manner identical to that of tubes 22 and 24.

The cathode and anode, respectively, of tubes 22 and 24 are connected via path 30 to the grid 32 of an amplifier tube 34. Tube 34 is included in one of the stages of an R. F. amplifier 36. Radio frequency energy is applied to grid 32 of tube 34 by means of an input transformer 38 and grid resistor 4d. The output of amplifier tube 34 is applied to the primary winding of coupling transformer 42 and, hence, to the grid 44 of a second amplifier tube 46. The cathode and anode, respectively,

2,824,959 Patented Feb. 25, 1958 of gaseous discharge tubes 26 and 28 are connected via path 48 and the secondary winding of transformer 42 to grid 44.

The positive terminal of voltage source 12 is grounded at point 49\and, hence, is connected to the cathodes of tubes 34 and 46. It becomes apparent, therefore, that upon conduction in tubes 22 and 24 a negative bias will be applied to grid 32 via path 30 and the secondary winding of transformer 38. Likewise, upon conduction in tubes 26 and 28, a negative bias will be applied to grid 44 via path 48 and the secondary winding of transformer 42. The voltage of this bias may be controlled by the selection of the types of gaseous discharge tubes chosen for positions 22 and 24 and also for positions 26 and 28. Resistors 5t) and 52 are provided to insure that gaseous discharge tubes 22 and 24 fire coincidentally with gaseous discharge tubes 26 and 28. If resistors 5 and 52 were omitted, one of the pairs of discharge tubes might fire before the other, thereby producing voltages which would prevent discharge of said other tubes. For example, if tubes 22 and 24 should fire first without resistors 50 and 52 in the circuit, the voltage on the cathode of tube 23 might be raised sufiiciently to prevent it from firing. Likewise, the voltage on the anode of tube 26 might be lowered sufficiently to prevent it from firing. If only one pair of series connected gaseous discharge tubes should be used, as for example, tubes 22 and 24, resistor 59 could be omitted and replaced by a direct connection.

Conduction through tubes 22, 24, 26 and 28 is controlled by the voltage applied to grid 54 of tube 10. This voltage is in the form of positive D. C. pulses as shown. Each voltage pulse is produced when a telegraph key, not shown, is in key-down position (i. e., when the key is closed). The polarities developed across resistors 16 and 13 are as shown. During key-down position tube 10 conducts and increases the voltage drop across resistors 16 and 18. The increased positive voltage developed by resistor 18 is applied to the cathodes of gaseous discharge tubes 24 and 28, and the increased negative voltage developed by resistor 16 is applied to the anodes of tubes 22 and 26. These voltages are of sufiicient magnitude to extinguish or cut oiT the gaseous tubes. With the gaseous discharge tubes 22 and 24 cut-oh or extinguished, there will be no blocking bias voltage applied to grid 32 via path 30 and transformer secondary 38. This condition will allow tube 34 to conduct. Likewise, with gaseous discharge tubes 26 and 28 cut-ofi or extinguished there will be no blocking bias voltage applied to grid 44 via path 48 and transformer secondary 42. This condition will allow tube 46 to conduct.

During key-up position, (i. e., when the telegraph key is open), the positive keying voltage is removed from grid 54, thereby reducing current flow through tube 10. As the current flow through tube iii is reduced, the voltage drops across resistors 16 and 18 are decreased until a point is reached where the voltage across gaseous discharge tubes 22 and 24 is increased sufficiently to allow them to fire. A negative voltage is now applied to the grids of tubes 34 and 46 such that they are cut off. Thus, during key-up position, tubes 34 and 46 are cut off; and during key-down position the tubes conduct.

The circuit is designed so that the gaseous discharge tubes will be cut oil? even though the magnitude of the voltage pulses applied to grid 54 should vary over a wide range. Because of the well-known inherent characteristics of gaseous discharge tubes, they establish a substantially constant voltage drop regardless of the current flow therethrough; and, therefore, a bloclc ng voltage of constant magnitude is applied to grids 32 and 44 during keyup position.

In the present embodiment the blocking voltage is ap-,

plied to the grids of a pair of amplifier tubes. However,

the blocking voltage maybe applied to the grid of'thetoscillator tube of a transmitter if' desired. The amplification stages employed may beeither class A, class B or class Q, depending upon requirements. Tube '34 in the present embodiment is operated class A, whereas tube'46 is operated class C. The necessary bias for these'tubes a The present invention therefore provides a m eans for applying a blocking voltage of constant magnitude'to thegrids of one or more vacuum tubes regardiesssof the variations; in magnitude of an available keying voltage 'sourcet Although the invention has been described in connection with a specific embodimenait will be appar- .ent to-those skilled in the art that various changes in 7 form and arrangement of parts can be made to suit requirements without departing from the spirit and sco'peof the invention. a

I claim as my invention: 7

l. A-system for applying and removing 'a blocking voltage at the grid of a vacuum tube comprising an 'electron discharge device having an anode, a cathode, and at least one grid included'therein, means for applying a pulsed voltage tothe grid of said device,1a source offanode voltage forasaid'device, a first resistor connecting the anodeof said discharge device to the positiv'e'termina'l of said voltage source, ,a'second resistor connecting the cathode of said discharge device to the negative terminal of said voltage source, a first gaseous discharge tube having its anode connected to the positive terminal of :said voltage source through said first resistor, a second gaseous discharge tub'e having its cathode connected to the negative terminal of saidvoltage source through, said second resistonand'means connecting the cathode and anode of said first and'second, gaseous tubes respectively a to thejgridof said vacuum tube.

2. Thecombination claimed in claim l' wherein the vacuum tube has an anode and cathode included therein,

I and means connecting said cathode to the positive tere rninal of saidvoltage source. t

3. A system for applying and removing a blocking t voltage at the grids of 'a plurality of vacuum'tubes comprising an electron discharge device having an anode, a cathode and at least one grid included therein, means for applying a' pulsed voltagete the grid of said'device, a source of anode voltage for'said device, a first resistor a may be conveniently adjusted by varying the type of gas: 7

j 'eousdischargetubes used. Since grid 44' is normally f positive with'respectto the cathode of the tube 46 it may draw excessive grid current and'cause damage to the L tube." To prevent this conditionja fixed negative bias voltage produced by' resistor 16, is applied via path 56 to t voltage at the grid of a vacuumftube comprising an elec-' v tubes corresponding to the number of said vacuum tubes and having'their cathodesconnected to the negative terminal of saidvoltage source through said second resistor, means connecting the cathode of each discharge tube of said first plurality of discharge tubes to the anode of a corresponding diseharg e tube, of said second plurality of dischargetubes, and means connecting the re-' spective interconnected ahodeland'cathodeof cachpair of discharge tubesto thegrid of a'corresponding one of saidv acuurn tubes; t t a .7 1 v 4; Apparatus for applying and removing ablocking tro'n'di'scharge device having a control electrode included therein, a device for applying apulsed voltagto said control electrode, first means for"developing a'voltage,

which' becomes' increasingly positive as a function' of i current flow through'said discharge device, secondlmeans for developing a voltage which becomesincreasingly negative as a function of current flow ithroughsaiiddischaige' respectively to the grid ,of said vacuum tube.

5. Apparatus for applying andremoving a blocking I voltage at the grid of a vacuum tube comprising an electron discharge device havinga'cQntrQI electrode in H cluded therein, a device for'applying a pulsed voltage" to a said control electrode, firs'tme'ans for developing 'a voltage whichb'ecomesincreasinglypositive'as current'flow t through said discharge device increases, second means'for' developing a voltage Which becomes increasingly nega-L tive as current flow through. said discharge' device im.

creases, a pairof unidirectional'current devices, positive and negative terminals for each of said unidirectional cur' rent devices,'means for applying the voltage developed by said first means'to the negative 'ter'minal'of a'first of connecting the anode of said discharge device to the positive terminal of said voltagetsource, a second resistor connecting the cathode of said discharge device'to'the negative terminal of said'voltage source, a first plurality of said vacuum tubes and having their anodes connected to the positive terminal of said voltage source *through *saidrfirst resistor, asecond plurality of gaseous discharge a gaseous discharge tubes corresponding to the number'cf said unidirectional current'devices," means 'for applying the voltage developed by said second means to the posi tive' terminal ofasecond of said unidirectional current devices, and means connecting the positive'and negative 1 terminals of said first and second unidirectional, current devices respectively to the grid, of said vacuum tube;

References Cited in thefile of this patent :UNITED STATES PATENTS 'Levy Apr. 26, 1949 2,593,350 7 Seybold Apr; '15, 1952 2,597,013 Marchetti May 20," 1952 2,644,088 Cooper, et a1. June 30, 1953 2,696,557 Gray Dec.;7, 1954 Armstrong 11111614, 1955 

